FIGS. 1A and 1B are copies of FIGS. 2A and 2B of European Patent No. EP1076366 (incorporated by reference). FIGS. 1A and 1B are a cross-section view and a top view of a monolithic bidirectional switch. Only the left-hand portions of FIGS. 1A and 1B will be discussed, each of these portions being delimited from the right-hand portion by a dotted line D. These left-hand portions correspond to a one-way switch Th1 having its gate referenced to main back side electrode A1.
Switch Th1 comprises a lightly-doped N-type silicon substrate 1. The back side of substrate 1 is covered with a P-type doped layer 2 forming the anode of the switch. An anode metallization M1 covers layer 2 and forms main back side electrode A1. The lateral surfaces of substrate 1 are totally covered with a P-type doped wall 7.
A P-type doped well 4 is formed from the front surface of substrate 1. A heavily N-type doped region 3 is formed in the upper portion of well 4. A cathode metallization M2 covers the upper surface of region 3 and forms the main front side electrode A2.
A P-type doped well 9 is also formed from the upper surface of substrate 1. Well 9 has, in top view, a rectangular shape and is in contact along its entire length and its small sides with P-type wall 7, as shown in FIG. 1B. A heavily-doped N-type gate region 8 is formed in the upper portion of well 9. A metallization M3 covers the upper surface of region 8 and forms gate electrode G. In this type of structure, gate electrode G is referenced to back side electrode A1, which forms the anode of the switch.
Emitter short-circuits may be formed in N-type doped cathode region 3. Similarly, an N-type doped channel stop region may be formed in substrate 1 around well 4. The emitter short-circuits and the channel stop region are not shown in FIGS. 1A and 1B. The operation of this switch is disclosed in detail in patent European Patent No. EP1076366. For the turning-on, while a negative voltage is applied to electrode A2 with respect to electrode A1, a negative voltage is applied to gate G with respect to electrode A1. A gate current ib flows between the gate and the anode and turns on an auxiliary thyristor Tha, formed by layer 2, substrate 1, well 9, and region 8. Thyristor Tha then conducts a current ic and turns on switch Th1. A current ITh1 then runs through switch Th1.
It would be desirable to be able to at least partly improve certain aspects of known bidirectional switches, and in particular their dV/dt behavior.